High surface area sol-gel route prepared hydrogenation catalysts

ABSTRACT

This invention concerns novel compositions, useful as hydrogenation catalyst, said compositions comprising metals and metal ions such as ruthenium (Ru) or palladium (Pd) dispersed in and distributed throughout a matrix comprising an inorganic or silicon oxide network. The catalyst may be prepared by the sol-gel method; a solution of at least one catalytic metal compound is added to a solution of at least one metal alkoxide selected from Al, Ti, Nb, Zr, Ta, Si and other inorganic alkoxides, and then gelling the mixture. Promotors such as rhenium (Re), molybdenum (Mo) and tin (Sn) may be added. The catalyst may be used in the reduction of metallic acid or gamma-butyrolactone to tetrahydrofuran (THF) and 1,4-butanediol (BDO).

This application is a 371 of PCT/US00/03175 filed Feb. 8, 2000, whichclaims the benefit of Provisional Application No. 60/119,255 filed Feb.9, 1999.

FIELD OF THE INVENTION

This invention concerns novel compositions, useful as catalysts, saidcompositions comprising metals and metal ions, such as ruthenium (Ru)and palladium (Pd), incorporated in an inorganic matrix comprising aninorganic oxide network. Catalyst activity is enhanced versus analogoussupported metal catalysts.

TECHNICAL BACKGROUND

E. I. Ko, in the Handbook of Heterogeneous Catalysis, ed. by G. Ertl etal, reviews generally the use of sol-gel processes for the preparationof catalytic materials. There is no disclosure of nor suggestion ofruthenium or rhenium containing catalysts.

U.S. Pat. No. 4,622,310 discloses inorganic phosphate aerogels. Theutility stated is as porous inert carrier materials (supports) inpolymerization and copolymerization processes. Use of the inorganicphosphates as supports for elements in groups VIB, VIIB and VIII of thePeriodic Table is described. There is no disclosure nor suggestion ofincorporating the elements within the inorganic phosphate gel matrix.

U.S. Pat. No. 4,469,816 discloses a catalyst composition comprising auniform dispersion of individual metallic palladium particlesimpregnated onto, within and throughout an alumina aerogel supportprocesses for the preparation of catalytic materials. There is nodisclosure of nor suggestion of ruthenium or rhenium containingcatalysts.

U.S. Pat. No. 5,538,931 discloses a process for preparing a supportedcatalyst comprising a transition metal selected from palladium,platinum, nickel, cobalt or copper on an aerogel support.

DE-A 195 30 528 and DE-A 195 37 202 disclose catalysts comprisingruthenium dispersed in titania and zirconia sol-gel matrices,respectively. No promotors or co-calalysts are described.

SUMMARY OF THE INVENTION

This invention provides catalyst precursor compositions comprisingcatalytic species dispersed in and distributed throughout a high surfacearea matrix wherein, the catalytic species is selected from the groupconsisting of ruthenium and palladium, in the optional presence of apromoter selected from the group consisting of rhenium, molybdenum andtin.

The high surface area matrix material may be an inorganic oxide network,optionally prepared by the sol-gel route.

This invention further provides catalyst compositions comprising thereduced form of the above catalyst precursor compositions.

The catalyst precursor composition may further include a promoter.

Preferred promoters are selected from the group consisting of Rhenium,Molybdenum and Tin.

This invention further provides improved processes for the reduction ofmaleic acid to tetrahydrofuran (THF) and 1,4-butanediol (BDO) and forthe reduction of gamma butyrolactone to tetrahydrofuran and1,4-butanediol, the improvement consisting of the use of the catalystsof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns novel catalyst compositions containingmetals and metal ions, such as ruthenium (Ru) and palladium (Pd),incorporated into a matrix comprising inorganic oxides and oxyhydroxidesof Ti, Nb, Ta, Zr and Si, Al, and others.

As used herein, the term matrix means a skeletal framework of oxides andoxyhydroxides derived from the hydrolysis and condensation of alkoxidesand other reagents. The framework typically comprises 30% or more, byweight, of the total catalyst composition. As discussed below, porosityand microstructure can be controlled, in some cases, by syntheticparameters (i.e. pH, temperature), drying, and other heat conditioning.As used herein, the term microstructure means a description, bothphysical and chemical in nature, of the bonding of domains andcrystallites with each other and their arrangement and physicalappearance or morphology in a matrix or solid; this term also describesthe structure and morphology, that is bonding and physical appearance,of the other active cationic precursors which are included in thisinvention.

The catalytic species are dispersed in and distributed throughout a highsurface area matrix. Alternatively, the catalytic species may bereferred to as being “matrix incorporated”.

Certain promoter materials, for example rhenium (Re), molybdenum (Mo)and tin (Sn), may also be present. Typical preparations involve sol gelchemistry. It is understood that sol gel products can be typicallyincompletely condensed resulting in products bearing residual hydroxy oralkoxy groups.

The catalyst compositions of the present invention may be prepared byone step synthesis of alcogels in which hydrolyzable matrix precursorsare used in the presence of soluble metal salts and promoters. Thispreparative process is characterized by adding a solution of at leastone catalytic metal compound selected from the group consisting ofruthenium and palladium to a solution of at least one metal alkoxide,wherein the metal is selected from the group consisting of Al, Ti, Nb,Zr, Ta, Si and other inorganic alkoxides, and gelling the resultingmixture. The order of addition of reagents, nature of precursors andsolvents and the nature of gelling agents may be varied widely. The termgelling agent means a reagent that causes or facilitates the formationof a gel. It may be acidic, basic or neutral, such as of water.

General compositional ranges for the catalyst precursors herein are Ruand Pd from 0.1 to 20 wt %; the promoters Re and Sn from 0 to 20 wt %with the balance being the matrix material.

A typical preparation involves the incorporation of Ru, Pd, Sn, Mo or Resalts, or mixtures thereof, in an alkoxide solution of aluminum,silicon, titanium, zirconium, tantalum or niobium. The hydrolysis of thealkoxides can either be acid or base catalyzed. Hydrolysis of thealkoxide precursors is accompanied by condensation reactions. Under theproper conditions (pH, gelling agent, reactant ratios, temperature,time, solvent and solvent concentration), these can result in thepolymerization into an inorganic gel containing the desired catalyticspecies or precursors. In some cases, the catalytic species are eitherpart of the polymerization network, or are entrapped within the network.

A consequence of this method is that higher metal dispersion anduniformity can be achieved in the inorganic oxide matrix than isnormally attainable using more conventional synthetic methods.

The first step in the synthesis of gels consists of preparing solutionsof the gel precursors, which may be, but are not limited to, alkoxidesand other reagents and separate solutions containing protic solventssuch as water. The alkoxide solutions are mixed with the solutionscontaining the protic solvents, and the alkoxides will react andpolymerize to form a gel. The protic solvent can include water, withtrace acid or base as catalyst to initiate hydrolysis. As polymerizationand crosslinking proceeds, viscosity increases and the material caneventually set to a rigid “gel”. The “gel” consists of a crosslinkednetwork of the desired material which incorporates the original solventwithin its open porous structure. The “gel” may then be dried, typicallyby either simple heating in a flow of dry air to produce an aerogel orthe entrapped solvent may be removed by displacement with asupercritical fluid such as liquid CO₂ to produce an aerogel, asdescribed below. Final calcination of these dried materials to elevatedtemperatures (>200° C.) results in products which typically have veryporous structures and concomitantly high surface areas.

In the preparation of the catalysts of the present invention, the activemetal precursors and promoters can be added to the protic or thealkoxide containing solutions. After gelation, the metal salt or complexis uniformly incorporated into the gel network. The gel may then bedried and heated to produce xerogel or aergoel materials, as describedbelow.

Because of the synthetic technique and the physical appearance of thealcogels materials produced, it is clear that the precursor xerogels andaerogels contain active metals and promoters in a highly dispersedstate. Further processing to produce the final catalytic material mayinclude chemical reduction at low temperatures to produce the finalhighly dispersed material, or a combination of calcination cycles invarious media, including hydrogen, to produce the final active catalyst.Activation of the material can be performed on stream, under reactionconditions.

In the practice of this invention one or more inorganic metal alkoxidesor salts thereof may be used as starting material for preparing thegels. It is, however, preferred to utilize the metal alkoxides. Therhenium promoter can be added as perrhenic acid in water during thesynthesis of the xerogel. It can also be post-added as Re(CO)₅Cl to thehydrogenation reaction mixture during the reaction.

The inorganic metal alkoxides used in this invention may include anyalkoxide which contains from 1 to 20 carbon atoms and preferably 1 to 5carbon atoms in the alkoxide group, which are preferably soluble in theliquid reaction medium. In this invention, preferably, C₁-C₄ systems,ethoxides, n-butoxides or isopropoxides are used.

One of the criteria for the starting material are inorganic alkoxides ormetal salts which will dissolve in the specified medium or solvent.Commercially available alkoxides can be used. However, inorganicalkoxides can be prepared by other routes. Some examples include directreaction of zero valent metals with alcohols in the presence of acatalyst. Many alkoxides can be formed by reaction of metal halides withalcohols. Alkoxy derivatives can be synthesized by the reaction of thealkoxide with alcohol in a ligand interchange reaction. Direct

reaction of dialkylamides with alcohol also forms alkoxide derivatives.The medium utilized in the process generally should be a solvent for theinorganic alkoxide or alkoxides which are utilized and the additionalmetal reagents and promoters which are added in the single stepsynthesis. Solubility of all components in their respective media(aqueous and non-aqueous) is preferred to produce highly dispersedmaterials. By employing soluble reagents in this manner, mixing anddispersion of the active metals and promoter reagents can be nearatomic, in fact mirroring their dispersion in their respectivesolutions. The precursor xerogel thus produced by this process will behighly dispersed active metals and promoters. High dispersion results inprecursor particles in the nanometer size range or smaller.

Generally, the amount of solvent used is linked to the alkoxide content.A molar ratio of 26.5 ethanol/total alkoxide is typically used, althougha range of 5 to greater than 53 can be used. If a large excess ofalcohol is used, gelation will not generally occur immediately; somesolvent evaporation is needed. At lower solvent concentrations, it iscontemplated that a heavier gel will be formed having less pore volumeand surface area.

To prepare the catalysts of the present invention, water and any aqueoussolutions are added in a dropwise fashion to the alcohol solublealkoxide and other reagents, to induce hydrolysis and condensationreactions. Depending on the alkoxide system, a discernible gel point canbe reached in minutes or hours. The molar ratio of the total water added(including water present in aqueous solutions), can vary according tothe specific inorganic alkoxide being reacted.

Generally, a molar ratio of H₂O:alkoxide range of 0.1 to 20 is withinthe scope of this invention. However, ratios close to 5:1 for tantalumalkoxide, 4:1 for zirconium alkoxide and titanium alkoxides can be used.The amount of water utilized in the reaction can be that calculated tohydrolyze the inorganic alkoxide in the reaction mixture. A ratio lowerthan that needed to hydrolzye the alkoxide species will result in apartially hydrolyzed material, which in most cases will reach a gelpoint at a much slower rate, depending on the aging procedure and thepresence of atmospheric moisture.

The addition of acidic or basic reagents to the inorganic alkoxidemedium can have an effect on the kinetics of the hydrolysis andcondensation reactions, and the microstructure of the oxide/hydroxidematrices derived from the alkoxide precursor which entraps orincorporates the soluble metal and promoter reagents. Generally, a pHrange of 1-12 can be used, with a pH range of 1-6 preferred for theseexperiments.

After reacting to form the alcogels of the present invention, it may benecessary to complete the gelation process with some aging of the gel.This aging can range form one minute to over several days. In general,all alcogels were aged at room temperature in air for at least severalhours.

The solvent in the gels can be removed in several different ways:conventional drying, freeze and vacuum drying, spray drying, or thesolvent can be exchanged under supercritical conditions. Removal byvacuum drying results in the formation of a xerogel. An aerogel of thematerial can typically be formed by charging in a pressurized systemsuch as an autoclave. The solvent laden gel which is formed in thepractice of the invention is placed in an autoclave where it can becontacted with a fluid above its critical temperature and pressure byallowing supercritical fluid to flow through the solvent laden gel, soas to extract the solvent, until the solvent is no longer beingextracted by the supercritical fluid. In performing this extraction toproduce the aerogel material, various fluids can be utilized at theircritical temperature and pressure. For instance, fluorochlorocarbonstypified by Freon® brand fluorochloromethanes and ethanes, ammonia andcarbon dioxide are all suitable for this process. Typically, theextraction fluids are fluids which are gases at atmospheric conditions,so that pore collapse due to the capillary forces at the liquid/solidinterface are avoided during drying. The resulting material should, inmost cases, possess a higher surface area than the non-supercriticallydried materials.

The xerogels and areogels thus produced can be described as precursorsalts incorporated into an oxide or oxyhydroxide matrix. The hydroxylcontent is undefined at this point; a theoretical maximum corresponds tothe valence of the central metal atom. Hence, Ta₂(O_(2-x)(OH)_(x))₅possesses a theoretical hydroxyl maximum at x=2. The molar H₂O:alkoxideratio can also affect the final xerogel stoichiometry; in this case, ifH₂O:T_(a)<5, there will be residual —OR groups in the unaged gel.However, reaction with atmospheric moisture will convert these to thecorresponding —OH and —O groups upon continued polymerization anddehydration. Aging, even under inert conditions, can also affect thecondensation of the —OH, eliminating H₂O, through continuation ofcrosslinking and polymerization, i.e., gel formation.

The materials of the present invention are useful in hydrogenationreactions. Specific examples include hydrogenation of maleic acid totetrahydro-furan, butanediol and other products and hydrogenation ofgamma butyrolactone into the same or similar products. For the lattercase, additional rhenium (preferably used as rhenium carbonyl chloride)may be added to the hydrogenation reactions as co-catalyst. Thecompositions of the present invention are also useful for the reductionof 3-hydroxypropionaldehyde to 1,3-propane diol.

The experimental results obtained show the novelty and unexpectedresults of the current invention. In maleic acid hydrogenation,catalytic reactor tests show the titania and zirconia derived aerogelsystems containing ruthenium and rhenium are very active for maleic acidhydrogenation to THF. The THF STY (space time yield, mol/hr-kg catalyst)of the matrix incorporated material in ZrO₂ shows at least a3.5×increase in STY versus supported catalysts. In addition, the maleicacid conversion is increased 10 fold.

The improvement in the single step synthetic method is clearlydemonstrated by comparing Example 4, 1 wt % Ru, 4 wt % Re in ZrO₂aerogel with comparative Example 5, 1 wt % Ru, 4 wt % Re on preformedZrO₂ aerogel, presoaked in water prior to impregnation, and comparativeExample 6, prepared by impregnation, at incipient wetness, of rutheniumchloride and perrhenic acid on pre-formned ZrO₂ aerogel. Catalystsprepared by the process of this invention showed and STY of 44. 1,versus 12.9 and 4.3 for comparative Examples 5 and 6. The >350% increasein STY is accompanied by a ten-fold increase in % maleic acidconversion, as defined as follows:

conversion=(moles reactant initial-moles reactant final)/(moles

reactant initial)=(moles reactant converted)/(moles reactant initial).

This unexpected improvement is achieved when three components are addedin a single step synthesis to produce the gel as compared to individual,sequential additions or impregnations on pre-formed supports, asdescribed in the comparative examples.

The zirconia aerogel prepared by this matrix incorporation method issignificantly more active than a comparable catalyst prepared by themore conventional method of supporting soluble Ru and Re on, forexample, a preformed ZrO₂ aerogel.

A series of aerogels prepared at lower ruthenium loadings (1/3 wt %)show surprising activity for gamma butyrolactone (GBL) hydrogenation,especially when a soluble rhenium complex [Re(CO)₅Cl] is added with theaerogel catalyst.

Acid stability tests on titania and tantalum oxide aerogels, and reactortests on all catalyst systems, have shown that these catalysts areessentially stable towards dissolution in liquid maleic acid.

Typical N₂ BET surface areas for these aerogel materials are severalhundred m²/g.

Zirconium n-propoxide, titanium n-butoxide, and tantalum and niobiumethoxides produce the highest quality gels when dissolved in ethanol.

In the data presented herein, THF is tetrahydrofuran, BDO is1,4-butanediol, space time yield (STY) is defined as (mole THF+BDOproduct/hr-kg catalyst). Selectivity is defined as moles (THF+BDO)/mole(THF+BDO+byproducts). Conversion herein is defined as (moles reactantconverted)/(moles reactant initially present).

TABLE 1 Compositional, Reactor Data and Surface Area/Density for MaleicAcid Hydrogenation using Aerogel Catalysts THF + BDO molar Bulk SurfaceExample STY selectivity Density Area No. Composition (mol/hr-kg) (THF +BDO) (Hg, g/cc) (m²/g) 1 Ta₂O₅ aerogel — — — — 0.057 wt % Ru, 0.023 wt %Re, Ta₂O₅ aerogel 9.1 0.87 1.14 246 (i) reduced in H₂/He 11.2* 0.88 1.51— (ii) unreduced prior to use 11.6 0.89 — — 2 1 wt % Ru, 4 wt % Re,Ta₂O₅ aerogel 25.5 0.83 — 224 3 1 wt % Ru, 4 wt % Re, Nb₂O₅ aerogel 16.40.82 — — 4 1 wt % Ru, 4 wt % Re, ZrO₂ aerogel 44.1 0.30 — — 5 1 wt % Ru,4 wt % Re supported on preformed ZrO₂ 12.9 0.86 — — [COMP.] aerogelpresoaked in H₂O prior to impregnation 6 1 wt % Ru, 4 wt % Re supportedon pre-formed ZrO₂ 4.3 0.68 — — [COMP.] aerogel, prepared by incipientwetness 7 1 wt % Ru, 4 wt % Re, TiO₂ cohydrolysis aerogel 9.9 0.61 — — 8Ru/Re/Sn TiO₂ aerogel 4.3 0.71 — — *duplicate prepration

TABLE 2 Compositional, Reactor Data and Surface Area/Density for GBLHydrogenation with and w/out added Re(CO)₅Cl 100 mg catalyst, 20 mgRe(CO)₅Cl, 250° C., 2,000 psi Example Conversion THF Bulk densitySurface area No. Composition GBL selectivity (Hg, g/cc) (m²/g)  9 1/3 wt% Ru Ta₂O₅ aerogel + Re(CO)₅Cl 45.5 91.4 0.32 322 10 1/3 wt % Ru TiO₂aerogel + Re(CO)₅Cl 67.2 92.3 — 322 11 1/3 wt % Ru, 4/3 wt % Re ZrO₂aerogel + Re(CO)₅Cl 52.7 87 — 300 12 1/3 wt % Ru, 4/3 wt % Re, Nb₂O₅aerogel 26.3 18.2 — 465 13 1/3 wt % Ru, 4/3 wt % Re, TiO₂ aerogel 10.195.1 — 547 14 1/3 wt % Ru, 4/3 wt % Re, Ta₂O₅ aerogel 33.7 10.7 — 241 151 wt % Ru, 4 wt % Re Ta₂O₅ aerogel 57.2 87 — 224

EXAMPLES GENERAL PROCEDURES Example 1 0.057 wt % Ru, 0.023 wt % Re inTantalum Oxide Aerogel

12.18 ml of ethanol (Quantum Chemical, Newark, N.J. dehydrated,punctilious grade) was combined with 40.47 g of tantalum ethoxide,Ta(OEt)₅ (Aldrich, Milwaukee, Wis.) in an inert atmosphere N₂ drybox. Ina separate container, 0.0303 g of ruthenium trichloride (Aldrich,Milwaukee, Wis.) was combined with 0.073 g of rhenium heptoxide (Re₂O₇,Aldrich, Milwaukee, Wis.), 8.25 g of water and 12.18 ml of additionalethanol. 1.03 ml of glacial acetic acid (J. T. Baker, Phillipsburg,N.J.) and 1.03 ml of 70 wt % nitric acid (EM Sciences, (Gibbstown, N.J.)were added to the water mixture. The aqueous solution containing theruthenium chloride and rhenium oxide was added, in a dropwise fashion,to the tantalum alkoxide solution. After several minutes, a cloudyorange/semi-opaque gel formed. Aging at room temperature proceeded forseveral days prior to removal of solvent by supercritical CO₂. Thematerial was placed in a stirred autoclave and extracted in CO₂ undersupercritical conditions. CO₂ gas was purged over the catalyst for aperiod of 7 hours, at 40° C. and a pressure of 3500 psi. The materialproduced following the exposure was a free flowing powder. The samplewas evaluated as prepared for hydrogenation reaction chemistry. Noadditional drying or calcination steps were performed.

Example 2 1 wt % Ru, 4 wt % Re, Tantalum Oxide Aerogel

123.04 ml of isobutyl alcohol (Aldrich) was combined with 81.25 g oftantalum ethoxide, Ta(OEt)₅ (Aldrich) in an inert atmosphere N₂ drybox.In a separate container, 0.9712 g of ruthenium trichloride (Aldrich) wascombined with 2.42 of rhenium heptoxide (Re₂O₇, Aldrich), 18.15 g ofwater and 123.04 ml of additional isobutyl alcohol (Aldrich). 2.146 mlof glacial acetic acid (J. T. Baker) and 1.675 ml of 70 wt % nitric acid(EM Sciences) were added to the water mixture. The aqueous solutioncontaining the ruthenium chloride and rhenium oxide was added, in adropwise fashion, to the tantalum alkoxide solution. After several hours(72 hours), a dark brown, slightly opaque gel formed. Aging at roomtemperature proceeded after 12 days prior to removal of solvent bysupercritical CO₂. The material was placed in a stirred autoclave andextracted in CO₂ under supercritical conditions. CO₂ gas was purged overthe catalyst for a period of 7 hours, at 40° C. and a pressure of 3500psi. The material produced following the exposure was a free flowingpowder. The sample was evaluated as prepared for hydrogenation reactionchemistry. No additional drying or calcination steps were performed.

Example 3 1 wt % Ru, 4 wt % Re in a Niobium Oxide Aerogel

228.6 ml of ethanol (Quantum Chemical, Newark, N.J. dehydratedpunctilious) was combined with 95.15 g of niobium ethoxide, Nb(OEt)₅(Aldrich) in an inert atmosphere N₂ drybox. In a separate container,0.9708 g of ruthenium trichloride (Aldrich) was combined with 2.1765 gof rhenium heptoxide (Re₂O₇, Aldrich), 26.934 g of water and 228.6 ml ofadditional ethanol. 3.208 ml of glacial acetic acid (J. T. Baker) and2.506 ml of 70 wt % nitric acid (EM Sciences) were added to the watermixture. The aqueous solution containing the ruthenium chloride andrhenium oxide was loaded in a dropping funnel, and slowly added to aniobium alkoxide soluton which had been loaded into a 1 liter resinkettle with a three neck cap. The resin kettle and dropping funnel werepurged with N₂ gas during the addition. After several minutes, a clearred-brown gel formed. Aging at room temperature proceeded forapproximately 50 days prior to removal of solvent by supercritical CO₂.The material was placed in a stirred autoclave and extracted in CO₂under supercritical conditions. CO₂ gas was purged over the catalyst fora period of 7 hours, at 40° C. and a pressure of 3500 psi. The materialproduced following the exposure was a free flowing powder. The samplewas evaluated as prepared for hydrogenation reaction chemistry. Noadditional drying or calcination steps were performed.

Example 4 1 wt % Ru, 4 wt % Re in a Zirconium Oxide Aerogel

228.6 ml of ethanol (Quantum Chemical) was combined with 23.32 g ofzirconium n-propoxide (70 wt % in n-propanol, (Alfa, Ward Hill, Mass.),in an inert atmosphere N₂ drybox. In a separate container, 0.9 g ofruthenium trichloride (Aldrich) was combined with 2.0178 g of rheniumheptoxide (Re₂O₇, Aldrich), 21.55 g of water and 228.6 ml of additionalethanol. 2.566 ml of glacial acetic acid and 2.004 ml of 70 wt % nitricacid were added to the water mixture. The aqueous solution containingthe ruthenium chloride and rhenium oxide was added, in a dropwisefashion, to the tantalum alkoxide solution. The material was containedin a resin kettle, and was blanketed with flowing N₂. During theaddition, a pink, thick opaque colloid forms. Some separation of thematerial into two layers was noted (opaque bottom layer and purple uppersolution). The entire sample was aged for 40 days prior to solventextraction using supercritical CO₂. CO₂ gas was purged over the catalystin a stirred autoclave for a period of 7 hours, at 40° C. and a pressureof 3500 psi. A free flowing powder was produced. The sample wasevaluated as prepared for hydrogenation reaction chemistry. Noadditional drying or calcination steps were performed.

Example 5 (Comparative) 1 wt % Ru, 4 wt % Re Supported on a Pre-formedZirconium Oxide Aerogel

A zirconium oxide aerogel was prepared in the following manner. 382.21ml of ethanol (Quantum Chemical) was combined with 46.797 g of zirconiumn-propoxide (70 wt % in propanol, (Aldrich) in an inert atmosphere N₂drybox. In a separate container, 7.206 g of water and 382.31 ml ofadditional ethanol were added to 0.858 ml of glacial acetic acid (J. T.Baker) and 1.03 ml of 10 0.67 ml of 70 wt % nitric acid (EM Sciences)were added to the water mixture. The aqueous solution containing theacetic and nitric acids was added, in a dropwise fashion, to thezirconium alkoxide solution. The entire apparatus was blanketed withinert nitrogen. A gel point could be determined after approximately 8hours, after allowing some ethanol solvent to slowly evaporate. A cleargel formed having a very faint yellow tint. The material was aged forseveral days at room temperature prior to solvent extraction. Thematerial was placed in a stirred autoclave and extracted in CO₂ undersupercritical conditions. CO₂ gas was purged over the catalyst for aperiod of 7 hours, at 40° C. and a pressure of 3500 psi. The materialproduced following the exposure was a free flowing powder. Approximately10 g of the aerogel powder was additionally calcined at 120° C. air,overnight.

3 g of the sample was soaked in 3 ml of distilled water at roomtemperature for 18 hours. A solution of 0.7 g of Ruthenium Chloride(RuCl₃ 1.095 H₂O, Aldrich) and 0.164 g of rhenium heptoxide (Aldrich),and 3 grams of water were slowly added to the water-soaked aergel. Afterstirring, the mixture was dried at 120° C. in air overnight, withfrequent stirring until dried. 2.92 g of solid material was recovered.The dried powder was reduced in a H₂/He mixture to activate thecatalyst. 2.90 g of the aerogel was added to a quartz boat. The samplewas purged with 500 sccm N₂ gas at room temperature for 15 minutes, andwas then heated to 150° C. and held at 150° C. for 1 hr. At this point,100 sccm of H₂ gas was added to the gas mixture, and the materialreduced at 150° C. The sample was then heated to 300° C. for 8 hrs inthe H₂/He mixture. Prior to cooling, the sample was purged for 30minutes with flowing B2 The aerogel was then passivated, to preventreaction with air upon removal, by flowing 1.5% O₂ in N₂ over thecatalyst at room temperature for 30 minutes. (Final sample weight was2.55 g, following this procedure).

Example 6 (Comparative) 1 wt % Ru, 4 wt % Re Supported on Pre-formedZrO₂ Aerogel

Another portion of the same zirconium aerogel as prepared in Example 5was used for this example. The aerogel was dried overnight for 18 hrs at120° C. Ruthenium chloride and rhenium heptoxide were impregnated byincipient wetness. A pore volume of about of 0.5 cc/g was not exceededduring these impregnations.

In a 20 ml vial, a solution containing 0.071 g of Ruthenium Chloride(RuCl₃ 1.095 H₂O, Aldrich) and 0.164 g of rhenium oxide (Re₂O₇, Aldrich)was prepared in 1.5 ml of H₂O. To this solution, 3 grams of thezirconium aerogel described above was added. The material was allowed tostand at room temperature, for 1 hour, with occasional stirring. Thematerial was additionally dried at 120° C. in aiovernight with frequentstirring, until dry.

Reduction Schedule

A catalyst reduction/activation procedure, identical to that describedin previous example, was used. The dried powder was reduced in a H₂/Hemixture to activate the catalyst. 2.24 g of the aerogel was added to aquartz boat. The sample was purged with 500 sccm N₂ gas at roomtemperature for 15 minutes, and was then heated to 150° C. and held at150° C. for 1 hr. At this point, 100 sccm of H₂ gas was added to the gasmixture, and the material reduced at 150° C. The sample was then heatedto 300° C. for 8 hrs in the H₂/He mixture. Prior to cooling, the samplewas purged for 30 minutes with flowing H₂. The aerogel was thenpassivated, to prevent reaction with air upon removal, by flowing 1.5%O₂ in N₂ over the catalyst at room temperature for 30 minutes. (Finalsample weight was 2.02 g, following the reduction procedure).

Example 7 1 wt % Ru, 4 wt % Re in a Titanium Oxide Aerogel

305.85 ml of ethanol was combined with 136.14 g of titanium n-butoxide(Aldrich) in an inert atmosphere N₂ drybox. In a separate vessel, 0.7561g of ruthenium trichloride (Aldrich) was combined with 1.75 g of rheniumheptoxide (Re₂O₇, Aldrich), 28.824 g of water and 305.85 ml ofadditional ethanol. 3.43 ml of glacial acetic acid (J. T. Baker) and2.681 ml of 70 wt % nitric acid (EM Sciences) were added to the watermixture with stirring. The aqueous solution containing the rutheniumchloride and rhenium oxide was added, in a dropwise fashion, to thetitanium alkoxide solution. Gellation occurred after twenty four hours,at which point a clear, amber colored gel formed. Aging at roomtemperature proceeded after several days prior to removal of solvent bysupercritical CO₂. The material was placed in a stirred autoclave andthe solvent was extracted using CO₂ held under supercritical conditions.CO₂ gas was purged over the catalyst for a period of 7 hours, at 40° C.and a pressure of 3500 psi. The material produced following the exposurewas a free flowing powder. The sample was evaluated as prepared forhydrogenation reaction chemistry. No additional drying or calcinationsteps were performed.

Example 8 1.5 wt % Ru, 3 wt % Re, 0.6 wt % Sn in TiO₂ Aerogel

229.39 ml of ethanol was combined with 102.108 g of titanium n-butoxide(Aldrich) and 0.2421 g SnCl₂ (Alfa A16202, anhydrous, Ward Hill, Mass.)in an inert atmosphere N₂ drybox. In a separate container, 0.8515 g ofruthenium trichloride (Aldrich) was combined with 0.9856 g of rheniumheptoxide (Re₂O₇, Aldrich), 21.62 g of water and 229.39 ml of additionalethanol. 2.575 ml of glacial acetic acid (J. T. Baker) and 2.01 ml of 70wt % nitric acid (EM Sciences) were added to the water mixture. Theaqueous solution containing the ruthenium chloride, rhenium oxide andtin chloride was added, in a dropwise fashion, to the titanium alkoxidesolution. A clear, dark-amber solution forms upon addition of thehydrolysant. No reaction was noted under N₂ for 72 hours. After slowlyallowing the solvent to evaporate, over a period of several days, aclear, amber colored gel formed. The gel was allowed to age at roomtemperature for a period of 15 days. The material was placed in astirred autoclave and extracted in CO₂ under supercritical conditions.CO₂ gas was purged over the catalyst for a period of 7 hours, at 40° C.and a pressure of 3500 psi. The material produced following the exposurewas a free flowing powder. Occasionally larger, clear pieces formedwhich were ground to a powder. The sample was evaluated as prepared forhydrogenation reaction chemistry. No additional drying or calcinationsteps were performed.

Example 9 ⅓ wt % Ru Incorporated in Tantalum Oxide Aerogel

30.95 ml of isobutyl alcohol (Aldrich) was combined with 20.245 g oftantalum ethoxide, Ta(OEt)₅ (Aldrich) in an inert atmosphere N₂ drybox.In a separate container, 0.0768 g of ruthenium trichloride (Aldrich) wascombined with 6.30 g of water and 30.95 ml of additional isobutylalcohol. 0.74097 ml of glacial acetic acid (J. T. Baker) and 0.5854 mlof % nitric acid (EM Scienceswere added to the water mixture. Theaqueous solution containing the ruthenium chloride was added, in adropwise fashion, to the tantalum alkoxide solution. No reaction isobserved at the time of addition. A gel point could be determinedapproximately 30 minutes after the complete addition of the aqueoussolution. A very clear, dark-colored gel formed. Aging at roomtemperature proceeded after 11 days prior to removal of solvent bysupercritical CO₂. The material was placed in a stirred autoclave andextracted in CO₂ under supercritical conditions. CO₂ gas was purged overthe catalyst for a period of 7 hours, at 40° C. and a pressure of 3500psi. The material produced following the exposure was a free flowingpowder. The sample was evaluated as prepared for hydrogenation reactionchemistry. No additional drying or calcination steps were performed.

Example 10 0.333 wt % Ruthenium Incorporated in a Titanium OxideAerogel; Soluble Rhenium Carbonyl Chloride Added During ReactorEvaluation

10 57.81 ml of ethanol (Quantum Chemical) was combined with 50.89 g oftitanium n-butoxide (Aldrich) in an inert atmosphere N₂ drybox. In aseparate container, 0.0825 g of ruthenium trichloride, RuCl₃ 0.2 H₂O(Aldrich) was combined with 5.39 g of water and 57.81 ml of additionalethanol. 0.642 ml of glacial acetic acid (J. T. Baker) and 0.501 ml of70% nitric acid (EM Sciences were added to the water mixture. Theaqueous solution containing the ruthenium chloride was added, in adropwise fashion, to the titanium alkoxide solution. A dark solutionforms. A gel point could be determined after approximately 12 hours atroom temperature. The gel is clear and dark amber in color. Agingproceeded at room temperature after five days prior to removal ofsolvent by supercritical CO₂. The material was placed in a stirredautoclave and extracted in CO₂ under supercritical conditions. CO₂ gaswas purged over the catalyst for a period of 7 hours, at 40° C. and apressure of 3500 psi. The material produced following the exposure was afree flowing powder. The sample was evaluated as prepared forhydrogenation reaction chemistry. No additional drying or calcinationsteps were performed.

Example 11 ⅓ wt % Ru, 4/3 wt % Re in a Zirconium Oxide Aerogel; SolubleRhenium Carbonyl Chloride Added During Reactor Evaluation

145.32 ml of isobutyl alcohol w as combined with 46.64 g of zirconiumn-propoxide (70 wt % solution in n-propanol, Aldrich) in an inertatmosphere N₂ drybox. In a separate container, 0.087 g of rutheniumtrichloride RuCl₃ 0.2 H₂O (Aldrich) was combined with 0.217 g of rheniumtrioxide (ReO₃), 7.18 g of water and 72 ml of additional ethanol. 0.8554ml of glacial acetic acid (J. T. Baker) and 0.667 ml of 70 wt % nitricacid were added to the water mixture. The aqueous solution containingthe ruthenium chloride and rhenium oxide was added, in a dropwisefashion, to the zirconium alkoxide solution in air with stirring. A darkbrown, opaque gel forms immediately following the addition of thehydrolysant. Again at room temperature for five days prior to removal ofthe solvent by supercritical CO₂. The material was placed in a stirredautoclave and extracted in CO₂ under supercritical conditions. CO₂ gaswas purged over the catalyst for a period of 7 hours, at 40° C. and apressure of 3500 psi. The material produced following the exposure was afree flowing powder. The sample was evaluated as prepared forhydrogenation reaction chemistry. No additional drying or calcinationsteps were performed.

Example 12 ⅓ wt % Ru, 4/3 wt % Re in a Nb₂O₅ Aerogel

115.62 ml of ethanol was combined with 47.52 g of niobium ethoxide(Aldrich,)in an inert atmosphere N₂ drybox. In a separate container,0.14 g of ruthenium trichloride, RuCl₃ 0.2 H₂O (Aldrich) and 0.3504 g ofrhenium trioxide (Aldrich) were combined with 13.47 g of water and115.62 ml of additional ethanol. 1.604 ml of glacial acetic acid and1.25 ml of 70 wt % nitric were added to the water mixture. The aqueoussolution containing the ruthenium chloride and rhenium trioxide wasadded, in a dropwise fashion, to the niobium alkoxide solution. Withinminutes, a red gel (some white particle were noted). After 12 hours, thegel appeared to be dark red and clear. Aging proceeded at roomtemperature for eleven days prior to removal of solvent by supercriticalCO₂. The material was placed in a stirred autoclave and extracted in CO₂under supercritical conditions. CO₂ gas was purged over the catalyst fora period of 7 hours, at 40° C. and a pressure of 3500 psi. The materialproduced following the exposure was a free flowing powder. The samplewas evaluated as prepared for hydrogenation reaction chemistry. Noadditional drying or calcination steps were performed.

Example 13 ⅓ wt % Ru, 4/3 wt % Re Incorporated in a Titanium OxideMatrix

19.05 ml of ethanol was combined with 33.92 g of titanium n-butoxide(Aldrich) in an inert atmosphere N₂ drybox. In a separate container,0.0564 g of ruthenium trichloride, RuCl₃ 0.2 H₂O (Aldrich) and 0.1404 gof rhenium trioxide (Aldrich) were combined with 7.182 g of water and19.05 ml of additional ethanol. 0.855 ml of glacial acetic acid(Aldrich) and 0.688 ml of % nitric acid (EM Sciences) were added to thewater mixture. The aqueous solution containing the ruthenium chlorideand rhenium trioxide was added, in a dropwise fashion, to the niobiumalkoxide solution. A gel point could be realized immediately afteraddition. A clear, dark amber gel formed. Within five days, removal ofsolvent by supercritical CO₂ proceeded. The material was placed in astirred autoclave and extracted in CO₂ under supercritical conditions.CO₂ gas was purged over the catalyst for a period of 7 hours, at 40° C.and a pressure of 3500 psi. The material produced following the exposurewas a free flowing powder. The sample was evaluated as prepared forhydrogenation reaction chemistry. No additional drying or calcinationsteps were performed.

Example 14 ⅓ wt % Ru, 4/3 wt % Re in a Tantalum Oxide Matrix

61.32 ml of isobutyl alcohol was combined with 40.491 g of tantalumethoxide (Aldrich) in an inert atmosphere N₂ drybox. In a separatecontainer, 0.156 g of ruthenium trichloride, RuCl₃ 0.2 H₂O (Aldrich) and0.3884 g of rhenium trioxide (Aldrich) were combined with 8.978 g ofwater and 61.32 ml of additional ethanol. 0.8978 ml of glacial aceticacid and 0.835 ml of 70 wt % nitric acid were added to the watermixture. The aqueous solution containing the ruthenium chloride andrhenium trioxide was added, in a dropwise fashion, to the niobiumalkoxide solution. The apparatus was blanketed in nitrogen. A 1 literresin kettle, fittle with a three-neck flask was used. A clear solutionobtained. The gel point was reached within 15 minutes. A clear, darkred-amber gel (perhaps slightly cloudy) was formed. Aging proceeded atroom temperature for twelve days prior to removal of solvent bysupercritical CO₂. The material was placed in a stirred autoclave andextracted in CO₂ under supercritical conditions. CO₂ gas was purged overthe catalyst for a period of 7 hours, at 40° C. and a pressure of 3500psi. The material produced following the exposure was a free flowingpowder. The sample was evaluated as prepared for hydrogenation reactionchemistry. No additional drying or calcination steps were performed.

Example 15 1 wt % Ru, 4 wt % Re, in a Tantalum Oxide aerogel

123.04 ml of isobutyl alcohol was combined with 81.25 g of tantalumethoxide, Ta(OEt)₅ (Aldrich) in an inert atmosphere N₂ drybox. In aseparate container, 0.9712 g of ruthenium trichloride (Aldrich) wascombined with 2.42 g of rhenium heptoxide (Re₂O₇, Aldrich), 18.15 g ofwater and 123.04 ml of additional isobutyl alcohol. 2.146 ml of glacialacetic acid (J. T. Baker) and 1.675 ml of 70 wt % nitric acid (EMSciences) were added to the water mixture. The aqueous solutioncontaining the ruthenium chloride and rhenium oxide was added, in adropwise fashion, to the tantalum alkoxide solution. After several hours(72 hours), a dark brown, slightly opaque gel formed. Aging at roomtemperature proceeded after 12 days prior to removal of solvent bysupercritical CO₂. The material was placed in a stirred autoclave andextracted in CO₂ under supercritical conditions. CO₂ gas was purged overthe catalyst for a period of 7 hours, at 40° C. and a pressure of 3500psi. The material produced following the exposure was a free flowingpowder. The sample was evaluated as prepared for hydrogenation reactionchemistry. No additional drying or calcination steps were performed.

Procedure for the Hydrogenation of Maleic Acid Batch Stirred AutoclaveReactor System

The reactor is a 300 cc Autoclave Engineers stirred autoclave made ofHastelloy C. The autoclave is 1.8 inch ID by 7 inch high. It is stirredwith a magnetically driven stirrer, which is powered by an electricmotor. The stirrer impeller is 1.25 inch OD and has 6 paddles. There areseveral top ports, which are connected to a pressure cell, cooling coil,a thermowell, and dip tube with a 7 micron fritted filter for removingreactor samples under process pressure and temperature. The coolingcoil, thermowell and sample dip also serve as baffles to promoteturbulence in the liquid. The body of the reactor is heated with aheating mantle. For a test hydrogenation, the system is operated inbatch mode, with 125 g of aqueous reagent, 0.4 g catalyst, continuoushydrogen feed, 2000 psig, 250° C. and 1000 rpm agitation for 45 minutes.At the end of the run, the reactor was cooled, vented to atmosphericpressure and the products analyzed by gas chromatography and titrationfor acid content. Results of the hydrogenations are in Table 1.

Procedure Used for Hydrogenation of Gamma-butyrolactone (GBL) toTetrahydrofuran/butanediol

To a 5 ml autoclave was charged about 4 gm of GBL and 100 mg ofcatalyst. The autoclave was heated to 250° C. and maintained at 2000 psiwith hydrogen for 12 hours. At the end of the run, the reactor wascooled, vented to atmospheric pressure and the products analyzed by gaschromatography. Results of the hydrogenations are in Table 2.

What is claimed is:
 1. A catalyst precursor composition comprisingcatalytic species dispersed in and distributed throughout a high surfacearea matrix, wherein the high surface area matrix is an inorganic oxidenetwork, prepared by a sol-gel route, wherein the inorganic oxide isselected from the group consisting of titanium oxide, niobium oxide,tantalum oxide, zirconium oxide, and oxyhydroxide analogs thereof andwherein, the catalytic species is selected from the group consisting ofruthenium and palladium and further comprising a promoter selected fromthe group consisting of Rhenium, Molybdenum and Tin, and mixturesthereof.
 2. A catalyst composition comprising the reduced form of thecatalyst precursor composition of claim 1.